Automotive wind tunnel testing can be broadly divided into two categories: aerodynamic and environmental. Aerodynamic tests aim at duplicating the pressure field on the vehicle exterior, and include evaluating the resultant forces and moments acting on the vehicle. Since the local pressure is proportional to the square of the velocity, errors in the velocity distribution of the simulated flow field can have a significant effect on the test results, and velocity errors in the simulation must be maintained at very low levels. Environmental (or climatic) tests aim at simulating automobile heating and cooling characteristics, and include developmental work on the cooling system, on the HVAC system, and on the reliability of engine mechanical and electronic components under sustained high temperature operation. Since the convective heat flux is proportional to the velocity raised to the 0.8 power, the effect of an error in the local velocity of the simulated flow field is less significant, and consequently greater velocity deviations are acceptable during climatic tests. For this reason, environmental tunnels are built with smaller nozzle exit areas than aerodynamic tunnels, with testing conducted at higher blockage and with larger errors in the local velocity over the vehicle.
Many of the existing environmental test facilities use high blockage, open jet test sections, and can only simulate the air flow at the very front of the vehicle, i.e., at the radiator grill, to an acceptable accuracy. The quality of the flow simulation over the vehicle then rapidly deteriorates as the unconstrained flow undergoes a large over expansion. As a result, the air flow simulation around the vehicle becomes inadequate.
The objects of the present invention are to provide an improved environmental automotive wind tunnel, more particularly an environmental automotive wind tunnel with improved simulation of air flow around a vehicle and to enable a reduction in the physical size of the wind tunnel.
In accordance with the invention, a slotted wall extension to the nozzle exit area is positioned over a vehicle to constrain the air flow around the vehicle and improve the simulation up to the rear of the vehicle.
Addition of the slotted-wall extension to the open jet considerably improves the air flow simulation over the entire vehicle in environmental wind tunnels, even at large blockage.
As disclosed herein, the extension comprises a three-sided, structure with vertical side walls and a horizontal top wall. In a preferred embodiment, the extension is approximately 1.45 to 1.5 vehicle lengths (LC) long, and has aerodynamically spaced longitudinal slots. However, longer and shorter lengths or slotted-walls may be used with equivalent good results. The slotted-wall extension is mounted on wheels or casters so that it can be rolled into position over the passenger car being tested, with the upstream end butted up against the exit of the wind tunnel nozzle and the downstream end proximate the rear of the passenger car. The slots on the extension walls constrain the air flow around the vehicle and improve the simulation up to the rear of the vehicle. The slotted-wall extension can be rolled out of place when not in use.